Monitoring cerebral tissue oxygenation or oxygen consumption is critical for the management of patients with traumatic brain injury and patients undergoing cardiac by-pass surgeries. Insufficient cerebral tissue oxygen consumption over a few minutes can lead to irreversible, severe, neurological damage. Cerebral oxygen consumption can be estimated through the differences between arterial and cerebral venous blood oxygen saturation. Pulse Oximetry (such as Masimo Radical-7™) is the clinical standard for non-invasive monitoring of arterial blood oxygen saturation at the finger tip. However, the determination of cerebral venous blood saturation is conducted using highly invasive venous catheters such as the jugular vein bulb catheter. Non-invasive methods such as pulse oximtery cannot be used to obtain cerebral venous blood oxygenation because, unlike arterial vessels, venous blood vessels are passive and without pulsation.
Cerebral tissue oximetry has also been developed based on near infrared spectroscopy to non-invasively measure tissue oxygenation at various sites on the head (such as INVOS Cerebral Oximeter of Somanetics Inc.). However, it is difficult for light to penetrate through the skull and reach cerebral tissues. As a result, the device is limited to measuring only a small spot on the surface of the cortical tissue which does not necessarily represent the overall cerebral tissue oxygenation, e.g. especially tissues deep inside brain.
Accordingly, there is a need to develop a means to accurately and non-invasively determine cerebral tissue dynamics.